1. Field of the Invention
The present invention relates to a pressure sensor for sensing the presence of one or more packages on a belt-driven roller conveyor, and in particular to such a sensor which can be adjusted to detect extremely light weight packages such as empty paperboard boxes. A plurality of such pressure sensors control a like plurality of pneumatic cylinders, causing them to disengage the conveyor drive in individual respective conveyor zones in response to detection of such packages in one or more succeeding zones to place the associated zone in an accumulation mode.
2. Description of the Related Art
In power driven conveyors, it is frequently necessary to temporarily disconnect the driving mechanism from the conveyor to allow accumulation of conveyed packages. For example, in a belt-driven roller conveyor, such as is used for conveying paperboard boxes in an assembly or loading station, for example, it is often necessary to raise or lower a case stop to halt the motion of a box on the conveyor while it is being loaded. In such an instance, it is desirable to allow a number of boxes to accumulate behind the box being loaded. It is common to use some type of pressure sensor which detects the presence of one or more of the boxes, and which disengages a drive mechanism from the conveyor rollers in response to such a detection.
Prior art conveyor pressure sensors have tended to be spring loaded and, consequently, to have very restrictive threshold weight limitations. For example, it is common in the prior art for such pressure sensors to require a package to weigh 2 or more pounds before the sensor will reliably respond. Such sensors are not suitable for a conveyor where empty paperboard boxes or other very light weight packages, such as envelopes or trays, must be accumulated.
It is clear then, that an improved apparatus and method for sensing and accumulating light weight packages on a beltdriven roller conveyor is needed. Such an apparatus should be compact and inexpensive, extremely rugged, should reliably sense light weight packages on the conveyor but should not be subject to inadvertent tripping. For versatility, such a sensor should preferably have a sensitivity adjustment to allow the sensor to respond to a range of threshold package weights.